A great deal of work has been carried out over the past few years with the aim of defining standardised tools that will allow us to untangle this web. One of the researchers’ main objectives is to combine all the available tests with the goal of obtaining "automated classifiers" that don't rely on the human eye. This would allow them to determine “objective” probabilities regarding the possible level of residual consciousness in a patient, in terms of the pain they may feel and their chances of recovery.

Stimulate then compress

On 14 August 2013, the journal Science Translational Medicine published an article(4) concerning a new approach designed to objectively assess the level of consciousness in an individual by measuring the complexity of their brain’s response to a magnetic stimulus. This work was carried out by an international team including researchers from the universities of Milan, Sao Paulo, Wisconsin and Liège (Coma Science Group).

At the root of this research is a theory developed at the University of Wisconsin-Madison by Professor Giulio Tononi: the Information Integration Theory. It proposes a mathematical approach to consciousness. “According to this theory, a living subject may be unconscious for two reasons: either because the brain is only processing information locally, or because when it becomes active, it is as though it had been roused throughout without any differentiation between its various regions, thus producing no information at all”, Steven Laureys explains. Consciousness assumes that the brain has access to rich and integrated information.

The researchers also know that transcranial magnetic stimulation (TMS) stimulates or inhibits the brain depending on the area to which it was administered. In hospitals, for instance, it is commonly used when recording motor evoked potentials (MEP). Hence, if it is administered to excite motor neurons, we can induce an automatic movement in the limbs and measure how long it takes the nervous impulse to propagate to the activated muscles, via the central and peripheral motor routes.

However, the abovementioned international group developed a far more subtle approach. In the same way as the recording of motor evoked potentials, TMS is coupled with an electroencephalographic recording (EEG), but here, the neuroscientists are interested in the integration of information by the brain, and its connectivity, which brings into play billions of neurons and millions of billions of connexions. “There is currently no supercomputer that can process all this data”, Steven Laureys tells us. “Therefore, we have to compress the content of the information emanating from the brain in response to a magnetic perturbation. For this purpose, we use algorithms similar to those that we commonly use to compress digital images before sending them by email.”

(4) Adenauer G. Casali, Olivia Gosseries, Mario Rosanova, Mélanie Boly, Simone Sarasso, Karina R. Casali, Silvia Casarotto, Marie-Aurélie Bruno, Steven Laureys, Giulio Tononi, Marcello Massimini, A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior, Science Translational Medicine, 14/08/2013